FIG. 1 is an isometric view of a known blade tensioner assembly TA′ for tensioning the slack strand of an automotive camshaft timing and/or balance shaft chain drive system. FIGS. 1A and 1B are respective sectional views taken at lines 1A-1A and 1B-1B of FIG. 1, and FIG. 1C illustrates a portion of FIG. 1 partially broken away to reveal the underlying structures. A bracket B′, typically defined as a one-piece metal stamping, is fixedly secured to an engine block, head, or other engine structure using one or more bolts or other fasteners F. The bracket B′ includes a main wall W, that is usually vertically oriented, and reaction ramp R that projects transversely outward from the main wall W. The ramp R comprises a reaction surface S which is typically planar but could be curved (e.g., convex or concave). The bracket B′ also includes a ramp support flange RF that projects from wall W and that is connected to and extends from the ramp R. The support flange RF is often defined with curved shape as shown for added strength required for preventing deflection of the ramp R and/or main wall W. The bracket B′ further includes a lip L that extends upwardly from the ramp R so as to be parallel and spaced-apart from the main wall W. A channel C is defined by the main wall W, the reaction surface S, and the lip L.
In the illustrated embodiment, a cylindrical pivot pin P is connected to and projects outwardly from the main wall W at a location spaced from the ramp. The blade tensioner assembly TA′ further comprises a blade assembly BA′ including a first or pivot end BA1 pivotally mounted on the pin P and a second or free end BA2 located in the channel C. The blade assembly BA′ comprises a one-piece molded polymeric or “plastid” blade 10 and a one-piece metal leaf spring 12 secured to the blade 10. The blade 10, itself, comprises a first or pivot end 10a and a second or free end 10b. The first end 10a of the blade comprises a pivot boss 14 including a cylindrical aperture 14a defined therein and adapted to be closely received on the cylindrical pivot pin P with minimal clearance. In some known prior blade tensioner assemblies, a shoulder bolt is used in place of the pin P for pivotally mounting the blade assembly to the bracket (and also securing the bracket B′ to the engine). The second end 10b of the blade comprises a foot 16 that is adapted to be located in the channel C of bracket B′. The first and second ends 10a,10b of the blade 10 are connected by a spine or central portion 18 that comprises a chain engaging slide surface 18s that is convexly curved. The central portion 18 is dimensioned and conformed so that it is able to flex resiliently in response to forces Z1 exerted thereon by an associated chain sliding on surface 18s, with the chain moving from the upstream first end 10a of the blade 10 toward the downstream second end 10b of the blade. A first end of the central portion 18 is connected to the pivot boss 14 by a first connecting wall 15, and a second end of the central portion 18 is connected to the foot 16 by a second connecting wall 17.
Referring also more particularly to FIGS. 1A, 1B and 1C, it can be seen that the first end 10a of the blade comprises a first slot S1′ and the second end 10b comprises a second slot S2′. Opposite first and second ends 12a,12b of the spring 12 are respectively positioned in the first and second slots S1′,S2′, and a convexly curved central portion 12c of the spring 12 abuts the central portion 18 of the blade 10, on the opposite side from chain engaging surface 18s. The spring 12 exerts a biasing force Z2 (FIG. 1) on the central portion 18 of blade for counteracting the chain forces Z1 in order to tension the slack strand of the chain. Flexing movement of the blade central portion 18 in response to chain forces Z1 and the counteracting spring biasing force Z2 (i.e., in the directions Z1 and Z2) results in forward and backward oscillatory sliding movement of the foot 16 on the ramp surface S in the channel C and corresponding oscillatory angular movement of the pivot boss 14 about pivot pin P.
The ends 12a,12b of the spring 12 are captured in the slots S1′,S2′ on an inner side by the wall W and on the opposite outer side by walls SW1,SW2 of the blade 10, respectively. The bracket lip L and wall SW2 include respective apertures PA1,PA2 (FIG. 1C) adapted for insertion of a pin (not shown) for fixedly securing the foot 16 of the blade 10 in the bracket channel C during shipping, handling and installation of the tensioner assembly TA′, and the pin must be removed from the apertures PA1,PA2 prior to use of the tensioner assembly TA′.
As is apparent in FIGS. 1A and 1B, the requirement to include the spring capturing walls SW1,SW2 leads to the slots S1′,S2′ being asymmetric in the sense that the walls SW1,SW2 are located on the outer side of the slots S1′,S2′, but not on the inner side of the slots S1′,S2′. The slots S1′,S2′ must remain open on the inner side opposite the walls SW1,SW2 in order to insert the spring 12 and also to allow for injection molding the blade 10 with walls slots SW1,SW2. These walls SW1,SW2 have been found to lead to regions of undesired stress concentration in the blade 10, particularly at the pivot end 10a in the wall connecting the pivot boss 14 to the central portion 18.